Not Applicable.
This invention relates generally to mechanical apparatus and more particularly to mechanical apparatus having pre-determined degrees of freedom and associated constrained degrees of freedom.
As is known, motion can be described as having six degrees of freedom. The six degrees of freedom of motion are, in reference to rectangular Cartesian axes, linear motion along the x-axis, the y-axis, and the z-axis, and rotational motion about the x-axis, the y-axis, and the z-axis. Various mechanical apparatus can move in one or more of the six degrees of freedom, while being constrained in others of the six degrees of freedom. Such mechanical apparatus are referred to herein as xe2x80x9cconstrained apparatus.xe2x80x9d
A two-axis flexure mechanism is a type of constrained apparatus for which a portion of the apparatus, herein referred to as a xe2x80x9cmotion stage,xe2x80x9d moves along a first axis in response to a first force applied along the first axis, and for which the motion stage moves move along a second axis in response to a second force applied along the second axis. The first and the second axes are often perpendicular to each other, but can also be at other relative angles. The first and the second forces are generated with respective first and second actuators, which can be solenoids, linear motors, piezoelectric actuators, lead screws, or the like. The two-axis flexure mechanism provides a motion stage that is essentially unconstrained within limits in two degrees of freedom in a motion plane, and may or may not be constrained in the four other degrees of freedom.
To provide the two-axis flexure mechanism, some conventional designs use a stacked assembly having a first linear motion stage stacked on top of a second linear motion stage. The first and the second linear motion stages can be single degree of freedom flexure mechanisms each providing translation along one respective axis. The stacked assembly is often referred to as a xe2x80x9cserial-kinematicsxe2x80x9d design. In the serial-kinematics design, the first linear stage has a first actuator and the second linear stage has a second actuator. With this arrangement, the first linear stage can move along the first axis and the second linear stage can move along the second axis, each linear stage able to move in translation with one degree of freedom. Here, the entire second stage moves in response to movement of the first stage. The motion stage, capable of moving in the motion plane, is coupled to the second stage. The serial-kinematics design requires that the second stage have an actuator that moves accordingly along with the second stage. Furthermore, the serial-kinematics design having the stacked arrangement requires a substantial height, the height perpendicular to the motion plane. These design factors result in serial-kinematics designs being relatively large and complex.
Another two-axis flexure mechanism uses a xe2x80x9cparallel-kinematicsxe2x80x9d design. The parallel-kinematics design usually provides a smaller mechanism than the serial-kinematics design described above. Like the serial-kinematics design, the parallel-kinematics design has a motion stage that can move in-a motion plane. Here, the first and second stages and actuators associated therewith are not stacked, but instead are disposed in the motion plane. However, the conventional parallel-kinematics design generates errors in the motion of the motion stage along the first axis and the second axis.
Error motions are characterized herein as xe2x80x9cdirect,xe2x80x9d xe2x80x9cparasitic,xe2x80x9d and xe2x80x9ccoupled.xe2x80x9d Direct error motion will be understood to be motion in a constrained degree of freedom in response to a force in the direction of the constrained degree of freedom. Parasitic error motion will be understood to be motion in a constrained degree of freedom in response to a motion in an unconstrained degree of freedom. Coupled error motion will be understood to be motion in one unconstrained degree of freedom in response to motion in another unconstrained degree of freedom.
Though smaller than a conventional serial-kinematics design, the conventional parallel-kinematics design generates motion having a variety of error motions. For example, the parallel-kinematics design generates coupled error motion along the second axis in response to movement of the first stage along the first axis. For another example, the conventional parallel-kinematics design generates parasitic error motion, otherwise constrained, as rotation about a third axis orthogonal to the first and second axes in response to unconstrained motion along the first or the second axes. Motion in the constrained degrees of freedom is often undesirable.
It would, therefore, be desirable to provide an apparatus having motion with only pre-determined degrees of freedom and associated constrained degrees of freedom, while minimizing direct, parasitic, and coupled error motions.
In accordance with the present invention, a motion apparatus includes a first, second, third and fourth flexure, and a first and second intermediate stage. The second and third flexures are coupled to a motion stage. The first, second, third and fourth flexures can be, but are not limited to, arm flexures, parallelogram flexures, or compound parallelogram flexures.
With this particular arrangement, the motion apparatus provides movement of the motion stage such that, when a force is applied to the first intermediate stage along a first axis, the motion stage moves substantially along the first axis. Also, when a force is applied to the second intermediate stage along a second axis, the motion stage moves substantially along the second axis.
In accordance with another aspect of the present invention, the motion apparatus further includes a fifth, sixth, seventh, eighth flexure, and a third and fourth intermediate stage. The sixth and seventh flexures are coupled to the motions stage. The fifth, sixth, seventh, eighth flexures can be arm flexures, parallelogram flexures, or compound parallelogram flexures.
With this particular arrangement, the motion apparatus provides movement of the motion stage such that, when a force is applied to the first or third intermediate stage along the first axis, the motion stage moves more substantially along the first axis. Also, when a force is applied to the second or fourth intermediate stage along the second axis, the motion stage moves substantially along the second axis. With this arrangement, error motions are reduced in comparison with the arrangement described above.
In accordance with yet another aspect of the invention, the first, second, third, fourth, fifth, sixth, seventh, and eighth flexures can be provided having arms comprised of a plurality of members, each member orthogonal to surrounding members.
With this particular arrangement, the motion apparatus provides movement of the motion stage in the direction of a third axis orthogonal to the first and the second axes, as well as rotation about the first and the second axis in response to forces applied, in the direction of the third axis, to one or more of the first, second, third and fourth intermediate stages. Where compound parallelograms are used for the flexures, the forces are applied instead to the third rigid body of the corresponding compound parallelogram flexures. Thus, a five degree of freedom motion apparatus is provided.
The motion apparatus provide motion stages having motion with only pre-determined degrees of freedom and associated constrained degrees of freedom, while minimizing direct, parasitic, and coupled error motions.